Polymeric materials used for electrical applications are required to meet stringent industry standards for flame retardant properties, good arc tracking resistance, while at the same time exhibiting good mechanical properties, such as tensile modulus and tensile strength. Increasingly stringent requirements also include meeting or exceeding such standards as the International Electrotechnical Commission (IEC) Glow Wire Flammability Index (GWFI) or Underwriters Laboratories, Inc. UL-94 flammability class rating.
Polyamide resins provide outstanding heat resistance and mold workability, making it useful for a variety of applications. However, polyamide shows poor flame resistance, rendering it necessary for the addition of flame retardants to provide the desired flame retardancy demanded by the particular application. Halogenated compounds and antimony compounds can provide a method to achieve flame retardancy in polyamide compositions. However the presence of bromine and antimony limit their application in the electrical and electronics segment, as well as appliances and transportations. Brominated flame retardants especially raise environmental concerns when the composition is burned.
Known, commercially available glass-reinforced halogen-free flame retardant polyamide materials cannot meet all the industry requirements. For instance, such materials fail to meet UL-94 V0 classification. U.S. Pat. No. 6,365,071 discloses a synergistic flame protection agent combination for thermoplastic polymers, especially for polyesters, containing as component A a phosphinic acid salt, a diphosphinic acid salt, as component B a nitrogen compound including, for example, triazine based compounds, cyanurate based compounds, allantoin based compounds, glycoluril based compounds, benzoguanamine based compounds, and the like. U.S. Patent Application 2004/0021135A1 discloses a halogen-free, flame retarder composition for use in a thermoplastic composition, in particular a glass fiber-reinforced polyamide composition, which flame retarder composition contains at least 10-90 mass percent phosphinate compound, 90-10 mass percent polyphosphate salt of a 1,3,5-triazine compound, and 0-30 mass % olefin copolymer. U.S. Patent Application No. 2004/0225040 discloses a flame retardant nanofilled combination of a thermoplastic polymer, a phosphinic salt, a diphosphinic salt, and an organic intercalated phyllosilicates.
There remains a need for halogen-free flame retardant polyamide compositions that exhibit good flame retardant properties, excellent arc tracking resistance properties, while at the same time retaining good mechanical properties.